1. Field of the Invention
This invention relates to a process for the production of compounds containing aldimine or ketimine groups by reacting compounds containing .beta.-ketoester groups with bis-aldimines or bis-ketimines with partial elimination of the aldehydes or ketones on which these compounds are based and to the preferred compounds containing ketimine groups obtained by this process.
2. Description of the Prior Art
Organic polyamines present in the form of aldimines or ketimines are valuable, potential reactants, which may be activated by heat and/or moisture, for organic polyisocyanates, polyanhydrides or polyepoxides in the production of plastics based on these starting materials (see, for example, DE-OS 1,520,139, DE-OS 1,719,121, DE-OS 3,710,963 or DE-OS 3,742,123).
To produce these blocked amines, primary amines are reacted with aldehydes or ketones by heating to temperatures above 60.degree. C.
Amines containing centers reactive to amino groups at elevated temperature, for example amines containing ester or carbonate groups, are not readily suitable as starting materials for this process because secondary reactions may take place. In addition, to convert the polyester, polyether or polycarbonate polyols known from polyurethane chemistry into the corresponding aldimine- or ketimine-terminated terminated derivatives by the old method, the terminal hydroxyl groups first have to be converted into primary amino groups by complicated methods.
A simple, universal process for the production of compounds containing aldimine or ketimine groups has now been found, in which compounds containing .beta.-ketoester groups are reacted with bis-aldimines or bis-ketimines in the presence of a catalytic quantity of water at comparatively low reaction temperatures in accordance with the following reaction scheme: ##STR1## In the less preferred use of aldimines as reactants for the .beta.-ketoesters, the substituent R.sub.3 is of course hydrogen.
Although the reaction between compounds containing .beta.-ketoester groups and bis-aldimines or bis-ketimines is known from U.S. Pat. No. 3,668,183, this patent is concerned with the production of adhesives using substantially equivalent quantities of the starting materials. It had not been expected that the reaction of the above-mentioned starting materials in accordance with the invention in a molar ratio of aldimine or ketimine groups to ketoester groups of approx. 2:1 would take place in the substantial absence of chain-extending or crosslinking reactions and would provide reaction products which have a distinctly lower viscosity than corresponding ketimine-terminated compounds obtained by the reaction of the corresponding polyamino compounds with ketones.